Abstract
Threshold voltage adjustment in threshold switching (TS) devices with HfO2/Al2O3 superlattice (by means of changing the cycle ratio of HfO2 to Al2O3 in atomic layer deposition) is investigated to implement a transparent cross-point array. TS devices with different cycle ratios (i.e., 3:1, 3:2, and 3:3) were fabricated and studied. The threshold voltage of the devices was increased from 0.9 V to 3.2 V, as the relative contents of Al2O3 layer in the superlattice were increased. At the same time, it is demonstrated that the off-resistance values of the devices were enhanced from 2.6 × 109 to 6 × 1010 Ω as the atomic layer deposition (ALD) cycle ratio of HfO2 to Al2O3 layer was adjusted from 3:1 to 3:3. However, the hold voltage and the on-current values were almost identical for the three devices. These results can be understood using the larger barrier height of Al2O3 layer than that of HfO2 layer.
Highlights
Transparent electronics have been ardently investigated in a variety of areas such as bioelectronics, environmental-engineering, display engineering, and wearable electronics as replacements and/or substitutions for conventional opaque electronics, because the optical transparency leads to functional merits in various applications [1,2,3,4,5]
When a TS device is connected to a non-volatile memory device in series, the device structure can show non-volatile memory characteristics, avoiding unexpected sneak leakage current [19]
When the threshold voltage is higher than the set voltage, the current becomes restricted by the high off-resistance of the TS device, even if the set voltage is applied to the non-volatile memory device
Summary
Transparent electronics have been ardently investigated in a variety of areas such as bioelectronics, environmental-engineering, display engineering, and wearable electronics as replacements and/or substitutions for conventional opaque electronics, because the optical transparency leads to functional merits in various applications [1,2,3,4,5]. When the threshold voltage is higher than the set voltage, the current becomes restricted by the high off-resistance of the TS device, even if the set voltage is applied to the non-volatile memory device For balancing those two voltage values, various methods (e.g., adding a diffusion barrier on a dielectric layer and/or changing a bottom electrode material) to adjust the threshold voltage of metal ion TS devices have been studied [22,23,24,25,28]. In this study, by varying the atomic layer deposition (ALD) cycle ratio of HfO2 and Al2O3 for HfO2/Al2O3 superlattice (HAO), the threshold voltage adjustment of TS devices on transparent indium tin oxide (ITO)/glass substrate is demonstrated for realizing transparent cross-point array. We expect that this experiment would help to expediate the development of a transparent cross-point array in the near future
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